1. Field of the Invention
This invention relates to a process and an apparatus for filling N.sub.2 gas into tires, and more particularly to a process and an apparatus for efficiently filling N.sub.2 gas inclusive of N.sub.2 rich gas having a high N.sub.2 concentration into tires such as passenger car tires, large-size vehicle tires (for truck and bus) and the like regardless of the kind of the tire used.
2. Description of Related Art
Since N.sub.2 gas is very durable to a temperature change, when N.sub.2 gas is filled into a tire, even if the temperature of the tire is raised during the high-speed running, severe service running or the like, the change of internal pressure in the tire is small and it is possible to prevent the lowering of the running performances and it is advantageous to improve the ride comfort. Therefore, the filling of N.sub.2 gas is adopted in special applications such as airplanes and F1 racing cars obliged to be run at a high speed.
Recently, it is generally and widely known that the filling of N.sub.2 gas into the tire develops an effect of preventing the degradation of rubber or wheel and the like. Further, the filling of N.sub.2 gas tends to be required by ordinary users with the advance of high tire performances. As a result, the filling of N.sub.2 gas is particularly carried out as a part of service in car shops, oil depots and the like. For this end, it is demanded to develop means for efficiently filling N.sub.2 gas into the tire with a relatively cheap filling cost.
As a filling system of N.sub.2 gas, there are known a method of using a commercially available cylinder filled with N.sub.2 gas for filling N.sub.2 gas into the tire, a method wherein only N.sub.2 gas is separated and purified with an industrial activated carbon while feeding compressed air through an air compressor for filling N.sub.2 gas, and a method of using a gas separation membrane wherein O.sub.2 and N.sub.2 are separated from air by utilizing a theory that permeation rates differ in accordance with a kind of gas components to thereby feed a high concentration N.sub.2 gas.
In the method of using the N.sub.2 filled cylinder, however, much labor is required in inventory control, carrying-in, carrying-out and the like of the cylinder and also it is required to ensure a setting place of the cylinder, so that this method is disadvantageous in view of the running cost. In the method using the industrial activated carbon, there is no inconvenience as mentioned above, but it is necessary that the activated carbon after the use over a certain time is subjected to a regeneration treatment for removing O.sub.2 adsorbed on the activated carbon once and hence the maintenance is inevitable. Particularly, when the filling of N.sub.2 gas is requested during the regeneration of the activated carbon, there is an inconvenience that such a request is not satisfied. And also, the method using the activated carbon has an advantage of setting the concentration of N.sub.2 gas to an arbitrary level, but when using the compressed air above 1000 kPa, a high pressure O.sub.2 gas (active gas) is gathered in a tank of a high pressure gas installation in view of its structure, so that it is disadvantageous to regulate a setting place of such an installation.
On the other hand, the method using the gas separation membrane does not cause the drawbacks as mentioned above and can relatively rapidly fill N.sub.2 gas, if necessary. And also, it is not required to use a tank gathering a high pressure O.sub.2 gas even when using a compressed air above 1000 kPa, so that the method can advantageously be used in wider fields without subjecting to the regulation for the high pressure gas installation. In this method, however, it can not be avoid that about 7% of O.sub.2 remains in a passenger car tire even when N.sub.2 gas having a concentration of 100% is filled into the tire so as to have an internal pressure of 200 kPa (even if air is merely taken out from the tire, air equal to atmospheric pressure is existent in the tire), so that it can not be said to more expect the effect by the filling of N.sub.2 gas. This is true in the above two methods. Particularly, a recommended internal pressure is higher in large size tires for truck and bus than that of the passenger car tire, so that a long time is unavoidably required in the filling of N.sub.2 gas into such a large size tire at the present. For this end, it is strongly demanded to solve these problems.